1. Field of the Invention
The present invention relates to an image projection apparatus (projector apparatus). More particularly the present invention relates to a projector apparatus using a liquid crystal panel etc. as an image displaying means. Specifically, the present invention relates to a reflection type image projection apparatus of a type reflecting light at a reflection type liquid crystal panel or other image displaying means and modulating the same.
2. Description of the Related Art
As the projector apparatuses using liquid crystal display devices (liquid crystal panels) for displaying images on image displaying means by modulating polarized beams, transmission type projector apparatuses passing modulated beams through the liquid crystal panels and modulating the modulated beams in the process of passage through the liquid crystal panels and reflection type projector apparatuses projecting modulated beams to the liquid crystal panels and modulating the projected modulated beams when reflected at the liquid crystal panels to change the polarization axes are known. The present invention particularly relates to the latter reflection type projector apparatuses.
As a reflection type projector apparatus, the one disclosed in for example Japanese Unexamined Patent Publication (Kokai) No. 8-15794 is known. The reflection type projector apparatus disclosed in Japanese Unexamined Patent Publication (Rokai) No. 8-15749 aims at a reduction of size and reduction of thickness by avoiding interference between the illumination system and the optical system as much as possible.
FIG. 7 is a view of the configuration of an optical system of a reflection type projector apparatus using a reflection type liquid crystal panel (LCOS: Liquid Crystal on Silicon) as the image display unit as a typical example of such a reflection type projector apparatus. The reflection type projector apparatus illustrated in FIG. 7 has, as a light source assembly for providing three primary colors, that is blue, green, and red, a lamp 201 for outputting a white color beam, a collimator lens 202, fly eyes lenses 203 and 204, a PS converting means 205 for converting a beam of for example a P-polarized component of the incident light to an S-polarized beam and outputting the same, a main condenser lens 206, a blue color reflection dichroic mirror 207, a green and red color reflection dichroic mirror 208, full reflection mirrors 209 and 210, and a green reflection dichroic mirror 211.
The reflection type projector apparatus further has a cross prism 224 and three polarized beam splitters (PBS) arranged around this cross prism 224, that is, a first polarized beam splitter 218, a second polarized beam splitter 219, and a third polarized beam splitter 223. The reflection type projector apparatus has a projection lens 225 at the side facing the second polarized beam splitter 219 across the cross prism 224. A condenser lens 212 is arranged at one side of the second polarized beam splitter 219, and a green color use liquid crystal reflection panel 213 and a ¼ wavelength plate 214 are arranged at the other side. A condenser lens 215 is arranged at one side of the first polarized beam splitter 218, and a red color use liquid crystal reflection panel 217 and a ¼ wavelength plate 216 are arranged at the other side. A condenser lens 220 is arranged at one side of the third polarized beam splitter 223, and a green color use liquid crystal reflection panel 222 and a ¼ wavelength plate 221 are arranged at the other side.
The three primary color beams, that is, the blue beam, the green beam, and the red beam, are output from the light source assembly as follows. The red beam is obtained from the white beam output from the main condenser lens 206 reflected at the green and red reflection dichroic mirror 208, reflected at the full reflection mirror 209, passed through the green reflection dichroic mirror 211, and striking the condenser lens 215. The green beam is obtained from the white beam output from the main condenser lens 206 reflected at the green and red reflection dichroic mirror 208, reflected at the full reflection mirror 209, reflected at the green reflection dichroic mirror 211, and striking the condenser lens 212. The blue beam is obtained from the white beam output from the main condenser lens 206 reflected at the blue reflection dichroic mirror 207, reflected at the full reflection mirror 210, and striking the condenser lens 220.
The green beam striking the condenser lens 212 is reflected at the second polarized beam splitter 219, passes through the ¼ wavelength plate 214, strikes the green color use liquid crystal reflection panel 213, is modulated there, then passes through the second polarized beam splitter 219, strikes the cross prism 224, and is projected from the projection lens 225 to a screen (not illustrated) located in front. The red beam striking the condenser lens 215 is reflected at the first polarized beam splitter 218, passes through the ¼ wavelength plate 216, strikes the red color use liquid crystal reflection panel 217, is modulated there, then passes through the first polarized beam splitter 218, strikes the cross prism 224, and is projected from the projection lens 225 to the screen (not illustrated) located in front. The green beam striking the condenser lens 220 is reflected at the third polarized beam splitter 223, passes through the ¼ wavelength plate 221, strikes the green color use liquid crystal reflection panel 222, is modulated there, then passes through the third polarized beam splitter 223, strikes the cross prism 224, and is projected from the projection lens 225 to the screen (not illustrated) located in front.
The light source unit providing the three primary color beams can be arranged above the above configuration or the like as illustrated in Japanese Unexamined Patent Publication (Rokai) No. 8-15794.
The reflection type projector apparatus using the first polarized beam splitter 218, the second polarized beam splitter 219, and the third polarized beam splitter 223 suffers from the problem that the brightness is insufficient since the F number of the illumination optical system cannot be made small.
Further, as illustrated in FIG. 5B, a polarized beam splitter suffers from the problem that the incident angle dependency is high. If there is an oblique incident beam, the transmission rate is lowered, so the contrast of the image projected from the projection lens 225 is lowered. In order to solve this, it becomes necessary to arrange parts of the optical system with a high precision and further finely adjust their positions.
Further, a polarized beam splitter has relatively large dimensions and is heavy in weight. As a result, there are limits to the reduction of the size of a reflection type projector apparatus.
When using polarized beam splitters, therefore, optical system is complex as a whole and the arrangement of the optical parts is difficult. Further, the mounting of the optical parts is difficult.
Further, a reflection type projector apparatus includes elements generating heat such as the lamp 201, the green color use liquid crystal reflection panel 213, the red color use liquid crystal reflection panel 217, and the green color use liquid crystal reflection panel 222, so measures for cooling these elements (heat dissipation measures) become necessary, but when a large number of parts are accommodated in a narrow space, it is difficult to sufficiently take heat dissipation measures or cooling measures.